Summary

Variable Lymphocyte Receptors (VLRs) are the adaptive immune receptors of jawless fish, which evolved adaptive immunity independent of other vertebrates. In lieu of the immunoglobulin-fold based T- and B-cell receptors, lymphocyte-like cells of jawless fish express VLRs (A, B or C) composed of leucine-rich repeats and are similar to toll-like receptors (TLRs) in structure, but antibodies (VLRB) and T cell receptors (VLRA, C) in function. Here we present the structural and biochemical characterization of VLR4, a VLRB, in complex with BclA, the immunodominant glycoprotein of Bacillus anthracis spores. Using a combination of crystallography, mutagenesis and binding studies, we delineate the mode of antigen recognition and binding between VLR4 and BclA, examine commonalities in VLRB recognition of antigens, and demonstrate the potential of VLR4 as a diagnostic tool for the identification of B. anthracis spores.

The 2009 H1N1 influenza pandemic is the first human pandemic in decades and was of swine origin. Although swine are believed to be an intermediate host in the emergence of new human influenza viruses, there is still little known about the host barriers that keep swine influenza viruses from entering the human population. We surveyed swine progenitors and human viruses from the 2009 pandemic and measured the activities of the hemagglutinin (HA) and neuraminidase (NA), which are the two viral surface proteins that interact with host glycan receptors. A functional balance of these two activities (HA binding and NA cleavage) is found in human viruses but not in the swine progenitors. The human 2009 H1N1 pandemic virus exhibited both low HA avidity for glycan receptors as a result of mutations near the receptor binding site and weak NA enzymatic activity. Thus, a functional match between the hemagglutinin and neuraminidase appears to be necessary for efficient transmission between humans and may be an indicator of the pandemic potential of zoonotic viruses.

Toll-like receptor 5 (TLR5) binding to bacterial flagellin activates NF-κB signaling and triggers an innate immune response to the invading pathogen. To elucidate the structural basis and mechanistic implications of TLR5-flagellin recognition, we determined the crystal structure of zebrafish TLR5, as a VLR-hybrid protein, in complex with the D1/D2 fragment of Salmonella flagellin, FliC, at 2.47 Å resolution. TLR5 interacts primarily with the three helices of the FliC D1 domain using its lateral side. Two TLR5-FliC 1:1 heterodimers assemble into a 2:2 tail-to-tail signaling complex that is stabilized by quaternary contacts of the FliC D1 domain with the convex surface of the opposing TLR5. The proposed signaling mechanism is supported by structure-guided mutagenesis and deletion analysis on CBLB502, a therapeutic protein derived from FliC.

Summary

The tad (tight adherence) locus encodes a protein translocation system that produces a novel variant of type IV pili. The pilus assembly protein TadZ (called CpaE in Caulobacter crescentus) is ubiquitous in tad loci, but is absent in other type IV pilus biogenesis systems. The crystal structure of TadZ from E. rectale (ErTadZ), in complex with ATP and Mg2+, was determined to 2.1 Å resolution. ErTadZ contains an atypical ATPase domain with a variant of a deviant Walker-A motif that retains ATP binding capacity while displaying only low intrinsic ATPase activity. The bound ATP plays an important role in dimerization of ErTadZ. The N-terminal atypical receiver domain resembles the canonical receiver domain of response regulators, but has a degenerate, stripped-down “active site”. Homology modeling of the N-terminal atypical receiver domain of CpaE indicates that it has a conserved protein-protein binding surface similar to that of the polar localization module of the social mobility protein FrzS, suggesting a similar function. Our structural results also suggest that TadZ localizes to the pole through the atypical receiver domain during early stage of pili biogenesis, and functions as a hub for recruiting other pili components, thus providing insights into the Tad pilus assembly process.

We conducted a genome-wide association study to search for risk alleles associated with Tetralogy of Fallot (TOF), using a northern European discovery set of 835 cases and 5159 controls. A region on chromosome 12q24 was associated (P = 1.4 × 10−7) and replicated convincingly (P = 3.9 × 10−5) in 798 cases and 2931 controls [per allele odds ratio (OR) = 1.27 in replication cohort, P = 7.7 × 10−11 in combined populations]. Single nucleotide polymorphisms in the glypican 5 gene on chromosome 13q32 were also associated (P = 1.7 × 10−7) and replicated convincingly (P = 1.2 × 10−5) in 789 cases and 2927 controls (per allele OR = 1.31 in replication cohort, P = 3.03 × 10−11 in combined populations). Four additional regions on chromosomes 10, 15 and 16 showed suggestive association accompanied by nominal replication. This study, the first genome-wide association study of a congenital heart malformation phenotype, provides evidence that common genetic variation influences the risk of TOF.

Most monoclonal antibodies (mAbs) to the influenza A virus hemagglutinin (HA) head domain exhibit very limited breadth of inhibitory activity due to antigenic drift in field strains. However, mAb 1F1, isolated from a 1918 influenza pandemic survivor, inhibits select human H1 viruses (1918, 1943, 1947, and 1977 isolates). The crystal structure of 1F1 in complex with the 1918 HA shows that 1F1 contacts residues that are classically defined as belonging to three distinct antigenic sites, Sa, Sb and Ca2. The 1F1 heavy chain also reaches into the receptor binding site (RBS) and interacts with residues that contact sialoglycan receptors and determine HA receptor specificity. The 1F1 epitope is remarkably similar to the previously described murine HC63 H3 epitope, despite significant sequence differences between H1 and H3 HAs. Both antibodies potently inhibit receptor binding, but only HC63 can block the pH-induced conformational changes in HA that drive membrane fusion. Contacts within the RBS suggested that 1F1 may be sensitive to changes that alter HA receptor binding activity. Affinity assays confirmed that sequence changes that switch the HA to avian receptor specificity affect binding of 1F1 and a mAb possessing a closely related heavy chain, 1I20. To characterize 1F1 cross-reactivity, additional escape mutant selection and site-directed mutagenesis were performed. Residues 190 and 227 in the 1F1 epitope were found to be critical for 1F1 reactivity towards 1918, 1943 and 1977 HAs, as well as for 1I20 reactivity towards the 1918 HA. Therefore, 1F1 heavy-chain interactions with conserved RBS residues likely contribute to its ability to inhibit divergent HAs.

Author Summary

Influenza infection kills thousands of people every year and causes major pandemics every few decades. The most lethal outbreak of influenza known was the 1918 H1N1 influenza pandemic that killed an estimated 20 to 100 million people. The 1918 virus was likely introduced into the human population from birds. We previously described five human neutralizing antibodies from survivors of the 1918 pandemic that bind the hemagglutinin (HA) surface antigen. Here, we define the binding sites of antibodies 1F1 and 1I20 on the 1918 HA and demonstrate that these overlap with the glycan receptor binding site. The glycan specificity differs between human and avian viruses for the linkages of the sialylated sugar receptors [human (α2–6) or avian (α2–3)]. 1F1 and 1I20 binds viruses that contain HA residues that mediate preference for α2–6 sialylated sugars. Three other control antibodies were not affected by preferences for the linkages of the sialylated sugar receptors because they bind elsewhere. Since the receptor-binding site is relatively conserved, this may explain the cross-reactivity of 1F1 and the enhanced binding of 1F1 and 1I20 to HAs with human receptor specificity.

Antibody Z13e1 is a relatively broadly neutralizing anti-HIV-1 antibody that recognizes the membrane proximal external region (MPER) of the HIV-1 envelope (Env) glycoprotein gp41. Based on the crystal structure of an MPER epitope peptide in complex with Z13e1 Fab, we identified an unrelated protein, IL-22, with a surface-exposed region that is structurally homologous in its backbone to the gp41 Z13e1 epitope. By grafting the gp41 Z13e1 epitope sequence onto the structurally homologous region in IL-22, we engineered a novel protein (Z13-IL22-2) that contains the MPER epitope sequence for use as a potential immunogen and as a reagent for detection of Z13e1-like antibodies. The Z13-IL22-2 protein binds Fab Z13e1 with a Kd of 73nM. The crystal structure of Z13-IL22-2 in complex with Fab Z13e1 shows that the epitope region is faithfully replicated in the Fab-bound scaffold protein; however isothermal calorimetry studies indicate that Fab binding to Z13-IL22-2 is not a lock-and-key event, leaving open the question of whether conformational changes upon binding occur in the Fab, or Z13-IL-22, or in both.

MtfA of Escherichia coli (formerly YeeI) was previously identified as a regulator of the phosphoenolpyruvate (PEP)-dependent:glucose phosphotransferase system. MtfA homolog proteins are highly conserved, especially among beta- and gammaproteobacteria. We determined the crystal structures of the full-length MtfA apoenzyme from Klebsiella pneumoniae and its complex with zinc (holoenzyme) at 2.2 and 1.95 Å, respectively. MtfA contains a conserved H149E150XXH153+E212+Y205 metallopeptidase motif. The presence of zinc in the active site induces significant conformational changes in the region around Tyr205 compared to the conformation of the apoenzyme. Additionally, the zinc-bound MtfA structure is in a self-inhibitory conformation where a region that was disordered in the unliganded structure is now observed in the active site and a nonproductive state of the enzyme is formed. MtfA is related to the catalytic domain of the anthrax lethal factor and the Mop protein involved in the virulence of Vibrio cholerae, with conservation in both overall structure and in the residues around the active site. These results clearly provide support for MtfA as a prototypical zinc metallopeptidase (gluzincin clan).

The HIV envelope (Env) protein gp120 is protected from antibody recognition by a dense glycan shield. However, several of the recently identified PGT broadly neutralizing antibodies appear to interact directly with the HIV glycan coat. Crystal structures of Fabs PGT 127 and 128 with Man9 at 1.65 and 1.29 Å resolution, respectively, and glycan binding data delineate a specific high mannose binding site. Fab PGT 128 complexed with a fully-glycosylated gp120 outer domain at 3.25 Å reveals that the antibody penetrates the glycan shield and recognizes two conserved glycans as well as a short β-strand segment of the gp120 V3 loop, accounting for its high binding affinity and broad specificify. Furthermore, our data suggest that the high neutralization potency of PGT 127 and 128 IgGs may be mediated by cross-linking Env trimers on the viral surface.

The hemagglutinin-neuraminidase (HN) protein of paramyxoviruses carries out three distinct activities contributing to the ability of HN to promote viral fusion and entry: receptor binding, receptor cleavage (neuraminidase), and activation of the fusion protein. The relationship between receptor binding and fusion triggering functions of HN are not fully understood. For Newcastle disease virus (NDV), one bifunctional site (site I) on HN′s globular head can mediate both receptor binding and neuraminidase activities, and a second site (site II) in the globular head is also capable of mediating receptor binding. The receptor analog, zanamivir, blocks receptor binding and cleavage activities of NDV HN′s site I while activating receptor binding by site II. Comparison of chimeric proteins in which the globular head of NDV HN is connected to the stalk region of either human parainfluenza virus type 3 (HPIV3) or Nipah virus receptor binding proteins indicates that receptor binding to NDV HN site II not only can activate its own fusion (F) protein but can also activate the heterotypic fusion proteins. We suggest a general model for paramyxovirus fusion activation in which receptor engagement at site II plays an active role in F activation.

A series of five PIM2 analogues were synthesized and tested for their ability to activate primary macrophages and modulate LPS signaling. Structural changes included replacement of the fatty acid esters of the phosphatidyl moiety of PIM2 with the corresponding ether or amide. An AcPIM2 analogue possessing an ether linkage was also prepared. The synthetic methodology utilized an orthogonally protected chiral myo-inositol starting material that was conveniently prepared from myo-inositol in just two steps. Important steps in the synthetic protocols included the regio- and α-selective glycosylation of inositol O-6 and introduction of the phosphodiester utilizing phosphoramidite chemistry. Replacement of the inositol core with a glycerol moiety gave compounds described as phosphatidylglycerol dimannosides (PGM2). Biological testing of these PIM compounds indicated that the agonist activity was TLR4 dependent. An ether linkage increased agonist activity, removal of the inositol ring enhanced antagonist activity and the presence of an additional lipid chain enhanced LPS-induced cytokine production in primary macrophages. Furthermore, the interruption of the LPS-induced TLR4/MD-2 2:2 signaling complex formation by PIM2 represents a previously unidentified mechanism involved in the bioactivity of PIM molecules.

Mammalian cells contain thousands of copies of mitochondrial DNA (mtDNA). At birth, these are thought to be identical in most humans. Here, we use long read length ultra-deep resequencing-by-synthesis to interrogate regions of the mtDNA genome from related and unrelated individuals at unprecedented resolution. We show that very low-level heteroplasmic variance is present in all tested healthy individuals, and is likely to be due to both inherited and somatic single base substitutions. Using this approach, we demonstrate an increase in mtDNA mutations in the skeletal muscle of patients with a proofreading-deficient mtDNA polymerase γ due to POLG mutations. In contrast, we show that OPA1 mutations, which indirectly affect mtDNA maintenance, do not increase point mutation load. The demonstration of universal mtDNA heteroplasmy has fundamental implications for our understanding of mtDNA inheritance and evolution. Ostensibly de novo somatic mtDNA mutations, seen in mtDNA maintenance disorders and neurodegenerative disease and aging, will partly be due to the clonal expansion of low-level inherited variants.

Filoviruses, including Marburg virus (MARV) and Ebola virus (EBOV), cause fatal hemorrhagic fever in humans and non-human primates. All filoviruses encode a unique multi-functional protein termed VP35. The C-terminal double-stranded (ds)RNA-binding domain (RBD) of VP35 has been implicated in interferon antagonism and immune evasion. Crystal structures of the VP35 RBD from two ebolaviruses have previously demonstrated that the viral protein caps the ends of dsRNA. However, it is not yet understood how the expanses of dsRNA backbone, between the ends, are masked from immune surveillance during filovirus infection. Here, we report the crystal structure of MARV VP35 RBD bound to dsRNA. In the crystal structure, molecules of dsRNA stack end-to-end to form a pseudo-continuous oligonucleotide. This oligonucleotide is continuously and completely coated along its sugar-phosphate backbone by the MARV VP35 RBD. Analysis of dsRNA binding by dot-blot and isothermal titration calorimetry reveals that multiple copies of MARV VP35 RBD can indeed bind the dsRNA sugar-phosphate backbone in a cooperative manner in solution. Further, MARV VP35 RBD can also cap the ends of the dsRNA in solution, although this arrangement was not captured in crystals. Together, these studies suggest that MARV VP35 can both coat the backbone and cap the ends, and that for MARV, coating of the dsRNA backbone may be an essential mechanism by which dsRNA is masked from backbone-sensing immune surveillance molecules.

Author Summary

Filoviruses, Marburg virus and five ebolaviruses, cause severe hemorrhagic fever that is characterized by suppression of the innate immune system. Important to immunosuppression is the viral protein VP35, which binds to and masks double-stranded (ds)RNA, a key signature of virus infection that is recognized by host sentry proteins like RIG-I and MDA-5. Previous crystal structures of VP35 from two ebolaviruses showed it to form an asymmetric dimer to cap the ends of dsRNA molecules. However, the question remained whether VP35 could mask remaining lengths of dsRNA between the ends from immune surveillance. Here we present the crystal structure of the dsRNA-binding domain (RBD) of Marburg virus VP35, alone and in complex with dsRNA. This crystal structure presents a very different arrangement of VP35s on dsRNA. Rather than binding only the ends, the Marburg virus VP35s spiral around the dsRNA backbone, continuously coating it. Additional biochemical experiments indicate that this continuous coating occurs in solution, and that like the ebolaviruses, Marburg virus VP35 is also able to cap the dsRNA ends, even though this was not apparent in the crystal structure. Together, this work illustrates how Marburg virus VP35 prevents recognition of dsRNA by backbone-sensing immune sentry molecules and provides an additional avenue for antiviral development.

The human nuclear factor related to kappa-B-binding protein (NFRKB) is a 1299-residue protein that is a component of the metazoan INO80 complex involved in chromatin remodeling, transcription regulation, DNA replication and DNA repair. Although full length NFRKB is predicted to be around 65% disordered, comparative sequence analysis identified several potentially structured sections in the N-terminal region of the protein. These regions were targeted for crystallographic studies, and the structure of one of these regions spanning residues 370–495 was determined using the JCSG high-throughput structure determination pipeline. The structure reveals a novel, mostly helical domain reminiscent of the winged-helix fold typically involved in DNA binding. However, further analysis shows that this domain does not bind DNA, suggesting it may belong to a small group of winged-helix domains involved in protein-protein interactions.

ABSTRACT

The influenza pandemic of 1918–1919 killed approximately 50 million people. The unusually severe morbidity and mortality associated with the pandemic spurred physicians and scientists to isolate the etiologic agent, but the virus was not isolated in 1918. In 1996, it became possible to recover and sequence highly degraded fragments of influenza viral RNA retained in preserved tissues from several 1918 victims. These viral RNA sequences eventually permitted reconstruction of the complete 1918 virus, which has yielded, almost a century after the deaths of its victims, novel insights into influenza virus biology and pathogenesis and has provided important information about how to prevent and control future pandemics.

Introduction

IKBKB (IKK-β/IKK-2), which activates NF-κB, is a substrate of the KEAP1-CUL3-RBX1 E3-ubiquitin ligase complex, implicating this complex in regulation of NF-κB signaling. We investigated complex component gene disruption as a novel genetic mechanism of NF-κB activation in non-small cell lung cancer (NSCLC).

Methods

644 tumor- and 90 cell line-genomes were analyzed for gene-dosage status of the individual complex components and IKBKB. Gene expression of these genes, and NF-κB target genes were analyzed in 48 tumors. IKBKB protein levels were assessed in tumors with and without complex or IKBKB genetic disruption. Complex component knockdown was performed to assess effects of the E3-ligase complex on IKBKB and NF-κB levels, and phenotypic importance of IKBKB expression was measured by pharmacological inhibition.

Results

We observed strikingly frequent genetic disruption (42%) and aberrant expression (63%) of the E3-ligase complex and IKBKB in the samples examined. While both adenocarcinomas and squamous cell carcinomas showed complex disruption, the patterns of gene disruption differed. IKBKB levels were elevated with complex disruption, knockdown of complex components increased activated forms of IKBKB and NF-κB proteins, and IKBKB inhibition detriments cell viability, highlighting the biological significance of complex disruption. NF-κB target genes were overexpressed in samples with complex disruption, further demonstrating the effect of complex disruption on NF-κB activity.

Conclusions

Gene dosage alteration is a prominent mechanism that disrupts each component of the KEAP1-CUL3-RBX1 complex and its NF-κB stimulating substrate, IKBKB. Here we show that, multiple component disruption of this complex represents a novel mechanism of NF-κB activation in NSCLC.

RP105–MD-1 modulates the TLR4–MD-2-mediated, innate immune response against bacterial lipopolysaccharide (LPS). The crystal structure of the bovine 1:1 RP105–MD-1 complex bound to a putative endogenous lipid at 2.9 Å resolution shares a similar overall architecture to its homologue TLR4–MD-2, but assembles into an unusual 2:2 homodimer which differs from any other known TLR-ligand assembly. The homodimer is assembled in a head-to-head orientation that juxtaposes the N-terminal leucine-rich repeats (LRRs) of the two RP105 chains, rather than the usual tail-to-tail configuration of C-terminal LRRs in ligand-activated TLR dimers, such as TLR1–2, 3 and 4. Another novel interaction is mediated by an RP105-specific Asn-linked glycan, which wedges MD-1 into the co-receptor binding concavity on RP105. This unique mode of assembly in RP105–MD-1 represents a new paradigm for TLR complexes and suggests a potential molecular mechanism for regulating LPS responses.

The V122I mutation that alters the stability of transthyretin (TTR) affects 3–4% of African Americans and leads to amyloidogenesis and development of cardiomyopathy. In addition, 10–15% of individuals over the age of 65 develop senile systemic amyloidosis (SSA) and cardiac TTR deposits due to wild-type TTR amyloidogenesis. As no approved therapies for TTR amyloid cardiomyopathy are available, the development of drugs that prevent amyloid-mediated cardiotoxicity is desired. To this aim, we developed a fluorescence polarization-based HTS screen, which identified several new chemical scaffolds targeting TTR. These novel compounds were potent kinetic stabilizers of TTR and prevented tetramer dissociation, unfolding and aggregation of both wild type and the most common cardiomyopathy-associated TTR mutant, V122I-TTR. High-resolution co-crystal structures and characterization of the binding energetics revealed how these diverse structures bound to tetrameric TTR. Our study also showed that these compounds effectively inhibited the proteotoxicity of V122I-TTR towards human cardiomyocytes. Several of these ligands stabilized TTR in human serum more effectively than diflunisal, which is one of the best known inhibitors of TTR aggregation, and may be promising leads for the treatment and/or prevention of TTR-mediated cardiomyopathy.

Current flu vaccines provide only limited coverage against seasonal strains of influenza viruses. The identification of VH1-69 antibodies that broadly neutralize almost all influenza A group 1 viruses constituted a breakthrough in the influenza field. Here we report the isolation and characterization of a human monoclonal antibody CR8020 with broad neutralizing activity against most group 2 viruses, including H3N2 and H7N7, which cause severe human infection. The crystal structure of Fab CR8020 with the 1968 pandemic H3 hemagglutinin (HA) reveals a highly conserved epitope in the HA stalk distinct from the epitope recognized by the VH1-69 group 1 antibodies. Thus, a cocktail of two antibodies may be sufficient to neutralize most influenza A subtypes and, hence, enable development of a universal flu vaccine and broad spectrum antibody therapies.

Advances in high-throughput, genome-wide profiling technologies have allowed for an unprecedented view of the cancer genome landscape. Specifically, high-density microarrays and sequencing-based strategies have been widely utilized to identify genetic (such as gene dosage, allelic status, and mutations in gene sequence) and epigenetic (such as DNA methylation, histone modification, and micro-RNA) aberrations in cancer. Although the application of these profiling technologies in unidimensional analyses has been instrumental in cancer gene discovery, genes affected by low-frequency events are often overlooked. The integrative approach of analyzing parallel dimensions has enabled the identification of (a) genes that are often disrupted by multiple mechanisms but at low frequencies by any one mechanism and (b) pathways that are often disrupted at multiple components but at low frequencies at individual components. These benefits of using an integrative approach illustrate the concept that the whole is greater than the sum of its parts. As efforts have now turned toward parallel and integrative multidimensional approaches for studying the cancer genome landscape in hopes of obtaining a more insightful understanding of the key genes and pathways driving cancer cells, this review describes key findings disseminating from such high-throughput, integrative analyses, including contributions to our understanding of causative genetic events in cancer cell biology.

Broadly neutralizing antibodies (bnAbs) against highly variable viral pathogens are much sought-after to treat or protect against global circulating viruses. We have probed the neutralizing antibody repertoires of four HIV-infected donors with remarkably broad and potent neutralizing responses and rescued 17 new monoclonal antibodies (MAbs) that neutralize broadly across clades. Many of the new MAbs are almost 10-fold more potent than the recently described PG9, PG16, and VRC01 bnMAbs and 100-fold more potent than the original prototype HIV bnMAbs1–3. The MAbs largely recapitulate the neutralization breadth found in the corresponding donor serum and many recognize novel epitopes on envelope (Env) glycoprotein gp120, illuminating new targets for vaccine design. Analysis of neutralization by the full complement of anti-HIV bnMAbs now available reveals that certain combinations of antibodies provide significantly more favorable coverage of the enormous diversity of global circulating viruses than others and these combinations might be sought in active or passive immunization regimes. Overall, the isolation of multiple HIV bnMAbs, from several donors, that, in aggregate, provide broad coverage at low concentrations is a highly positive indicator for the eventual design of an effective antibody-based HIV vaccine.

The crystal structures of an unliganded and adenosine 5′-monophosphate (AMP) bound, metal-dependent phosphoesterase (YP_910028.1) from Bifidobacterium adolescentis are reported at 2.4 Å and 1.94 Å, respectively. Functional characterization of this enzyme was guided by computational analysis and then confirmed by experiment. The structure consists of a PHP (Polymerase and Histidinol Phosphatase, Pfam: PF02811) domain with a second domain (residues 105–178) inserted in the middle of the PHP sequence. The insert domain functions in binding AMP, but the precise function and substrate specificity of this domain is unknown. Initial bioinformatics analyses yielded multiple potential functional leads, with most of them suggesting DNA polymerase or DNA replication activity. Phylogenetic analysis indicated a potential DNA polymerase function that was somewhat supported by global structural comparisons identifying the closest structural match to the alpha subunit of DNA polymerase III. However, several other functional predictions, including phosphoesterase, could not be excluded. THEMATICS, a computational method for the prediction of active sites from protein 3D structures, identified potential reactive residues in YP_910028.1. Further analysis of the predicted active site and local comparison with its closest structure matches strongly suggested phosphoesterase activity, which was confirmed experimentally. Primer extension assays on both normal and mismatched DNA show neither extension nor degradation and provide evidence that YP_910028.1 has neither DNA polymerase activity nor DNA proofreading activity. These results suggest that many of the sequence neighbors previously annotated as having DNA polymerase activity may actually be misannotated.

Influenza virus hemagglutinin (HA) is the viral envelope protein that mediates viral attachment to host cells and elicits membrane fusion. The HA receptor-binding specificity is a key determinant for the host range and transmissibility of influenza viruses. In human pandemics of the 20th century, the HA normally has acquired specificity for human-like receptors before widespread infection. Crystal structures of the H1 HA from the 2009 human pandemic (A/California/04/2009 [CA04]) in complex with human and avian receptor analogs reveal conserved recognition of the terminal sialic acid of the glycan ligands. However, favorable interactions beyond the sialic acid are found only for α2-6-linked glycans and are mediated by Asp190 and Asp225, which hydrogen bond with Gal-2 and GlcNAc-3. For α2-3-linked glycan receptors, no specific interactions beyond the terminal sialic acid are observed. Our structural and glycan microarray analyses, in the context of other high-resolution HA structures with α2-6- and α2-3-linked glycans, now elucidate the structural basis of receptor-binding specificity for H1 HAs in human and avian viruses and provide a structural explanation for the preference for α2-6 siaylated glycan receptors for the 2009 pandemic swine flu virus.

The Chillingham herd of wild Northumbrian cattle remains viable despite over 300 years of in-breeding and a near-homozygous nuclear genome. Here we report the complete mitochondrial DNA sequence using ultra-deep next generation sequencing. Random population sampling of ~ 10% of the extant herd identified a single mtDNA haplotype harbouring a unique bovine variant present in all other higher mammals (m.11789C/Y421H) which may contribute to their survival.

Highlights

► The Chillingham herd of wild Northumbrian cattle remains viable despite over 300 years of in-breeding and a near-homozygous nuclear genome. ► ~ 10% of the extant population have an identical mitochondrial genome with a unique bovine variant present in all other higher mammals (m.11789C/Y421H) which may contribute to their survival.